U.S. patent number 4,796,950 [Application Number 07/012,573] was granted by the patent office on 1989-01-10 for tilt mechanism, particularly for knee-tilt chair.
This patent grant is currently assigned to Haworth, Inc.. Invention is credited to Donald L. Cool, Fred C. Liebertz, Walter C. Mrotz, III.
United States Patent |
4,796,950 |
Mrotz, III , et al. |
January 10, 1989 |
**Please see images for:
( Certificate of Correction ) ** |
Tilt mechanism, particularly for knee-tilt chair
Abstract
The seat and pedestal of a chair are joined by a knee-tilt
mechanism which includes a first support fixed to the underside of
the seat adjacent the front edge thereof, and a second support
fixed to the pedestal and having a sidewardly extending support
tube arrangement. The first support has bearing hubs rotatably
engaged with the support tube to define a horizontal tilt axis. A
restoring mechanism is disposed within the second support for
exerting a restoring torque about the tilt axis for urging the seat
toward its horizontal position. The restoring mechanism, in the
preferred embodiment, employs a sleevelike spring member of an
elastomeric material disposed on the tilt axis for developing a
restoring torque which generally linearly increases as the seat
tilts away from the horizontal position. A second spring coacts
between the supports for generating a second restoring torque which
is additive with the first torque to effectively cause a torque
dwell to facilitate tilting beyond an intermediate position.
Inventors: |
Mrotz, III; Walter C. (North
Muskegon, MI), Cool; Donald L. (Holland, MI), Liebertz;
Fred C. (Twin Lake, MI) |
Assignee: |
Haworth, Inc. (Holland,
MI)
|
Family
ID: |
21755606 |
Appl.
No.: |
07/012,573 |
Filed: |
February 9, 1987 |
Current U.S.
Class: |
297/303.3;
248/608; 297/302.3; 297/302.4 |
Current CPC
Class: |
A47C
3/026 (20130101) |
Current International
Class: |
A47C
3/02 (20060101); A47C 3/026 (20060101); A47C
003/00 () |
Field of
Search: |
;297/302,303,304,305,306,300,301 ;248/608,609 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
490970 |
|
Mar 1953 |
|
CA |
|
933492 |
|
Sep 1955 |
|
DE |
|
1554058 |
|
Mar 1970 |
|
DE |
|
656782 |
|
May 1929 |
|
FR |
|
656957 |
|
Sep 1951 |
|
GB |
|
785194 |
|
Oct 1957 |
|
GB |
|
Other References
Herman Miller Brochure: "Equa A Chair For People Who Can't Sit
Still" 1984 16 pages. .
Herman Miller Brochure: "Equa Seating", 1985, 15 pages. .
Herman Miller Brochure: "We Hope You Enjoy Your New Equa Chair",
1984, 1 page. .
Herman Miller Magazine, "From Equa Seating to Seafood Linguini",
pages 31-36..
|
Primary Examiner: Zugel; Francis K.
Attorney, Agent or Firm: Flynn, Thiel Boutell &
Tanis
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. In a pedestal-type chair having a base assembly defining thereon
a pedestal which projects vertically upwardly in cantilevered
fashion, a seat structure having both a seat and a back, the seat
being disposed directly above the pedestal so that the latter has
its vertical centerline intersecting the seat adjacent the midpoint
thereof, and a knee-tilt mechanism connected between the pedestal
and seat and defining a substantially horizontally extending tilt
axis which extends sidewardly relative to the seat in the vicinity
of the front edge thereof for permitting the seat to be tilted
downwardly about the tilt axis from a substantially zero-tilt
position when the chair is unoccupied through a maximum tilt angle
to a lower tilt position when the chair is occupied, said tilt axis
being disposed a substantial distance forwardly from and in
nonintersecting relationship to the vertical centerline of said
pedestal, the improvement wherein said tilt mechanism
comprises:
a housing structure mounted on said pedestal adjacent the upper end
thereof and projecting forwardly therefrom toward the front edge of
said seat, and a support structure secured to said seat and
projecting downwardly therefrom adjacent but spaced slightly
rearwardly from the front edge thereof, said support and housing
structures having opposed parts which are relatively rotatably
supported on one another for defining said tilt axis;
first biasing means coacting between said housing and support
structures for imposing a restoring torque about said tilt axis
which normally urges said seat into said zero-tilt position, said
first biasing means including spring means for generating a
restoring torque which increases approximately linearly in
relationship to the angularity of seat tilt as the seat tilts from
the zero-tilt position toward the lower tilt position;
second biasing means coacting between said support and housing
structures for imposing a restoring torque about said tilt axis
which continuously urges said seat toward said zero-tilt position,
said second biasing means being operatively coupled between said
structures in generally parallel relationship with said first
biasing means so that said first and second restoring torques add
together for urging the seat toward said zero-tilt position;
said second biasing means including a spring unit hingedly
supported at one end about a first substantially horizontal pivot
axis and lever means hingedly supported at one end about a second
substantially horizontal pivot axis which is parallel with but
spaced sidewardly from said first pivot axis, one of said first and
second pivot axes being coaxially aligned with said tilt axis, and
cam means cooperating between the other end of said spring unit and
the other end of said lever means for creating said second
restoring torque, said cam means including cam follower means
associated with the other end of said spring unit, said cam means
also including a first elongated cam profile associated with the
other end of said lever means and a second elongated cam profile
stationarily associated relative to one of said structures, said
cam follower means being cooperatively engaged with and captivated
between said first and second elongated cam profiles.
2. A chair according to claim 1, wherein said first spring means
comprises a sleevelike torsion spring member constructed of a
rubberlike elastomeric material.
3. A chair according to claim 2, wherein said sleevelike spring
member surrounds and is nonrotatably coupled to a shaft which is
fixed to said support structure, said shaft extending along said
tilt axis, and pretorque adjusting means coupled between said
housing structure and an exterior wall of said sleeve-like spring
member for permitting the pretorque on said sleevelike spring
member when the chair is in said zero-tilt position to be
selectively adjusted.
4. A chair according to claim 3, wherein said lever means has the
one end thereof nonrotatably coupled to said support structure for
angular displacement about said tilt axis, said first cam profile
extending approximately radially of said lever means adjacent the
other end thereof, said spring unit being disposed so that its line
of force extends at a substantial angle to and in intersecting
relationship with the radially extending direction of said lever
means when the seat is in said zero-tilt position, said second cam
profile extending transversely with respect to the radial direction
of said lever means and also with respect to the line of force of
said spring unit.
5. A chair according to claim 4, wherein a bracket structure is
fixedly secured to said housing structure and includes a pair of
spaced and substantially parallel sidewalls which confine said
spring unit therebetween, said spring unit having a first pin at
said one end thereof, said first pin extending transversely between
and supported on said spaced sidewalls for defining said first
pivot axis, said sidewalls having a pair of second cam slots formed
therein and defining said second cam profiles, said lever means
including a pair of sidewardly spaced levers disposed respectively
adjacent said sidewalls, said last-mentioned levers having a pair
of first cam slots formed therein and defining said first cam
profiles, and said spring unit having a second pin associated with
the other end thereof and extending transversely between said
sidewalls so that opposite ends of said second pin project through
and are captivated by the respectively adjacent pairs of first and
second cam slots.
6. A chair according to claim 5, wherein said second cam profile as
defined by said second cam slot includes (1) a first profile
portion which is substantially linear for causing substantially
linear compression of said spring unit as the seat tilts from the
zero-tilt position to said intermediate position and (2) a second
profile portion which merges smoothly with said first profile
portion and controls compression of said spring unit as the chair
tilts from said intermediate position to said lower tilt position,
said second profile portion being generated on a radius having its
center located in close proximity to said first pivot axis.
7. A chair according to claim 1, wherein said lever means has the
one end thereof nonrotatably coupled to said support structure for
angular displacement about said tilt axis, said first cam profile
extending approximately radially of said lever means adjacent the
other end thereof, said spring unit being disposed so that its line
of force extends at a substantial angle to and in intersecting
relationship with the radially extending direction of said lever
means when the seat is in said zero-tilt position, said second cam
profile extending transversely with respect to the radial direction
of said lever means and also with respect to the line of force of
said spring unit.
8. In a pedestal-type chair having a base assembly defining thereon
a pedestal which projects vertically upwardly in cantilevered
fashion, a seat structure having both a seat and a back, the seat
being disposed directly above the pedestal so that the latter has
its vertical centerline intersecting the seat adjacent the midpoint
thereof, and a knee-tilt mechanism connected between the pedestal
and seat and defining a substantially horizontally extending tilt
axis which extends sidewardly relative to the seat in the vicinity
of the front edge thereof for permitting the seat to be tilted
downwardly about the tilt axis from a substantially zero-tilt
position when the chair is unoccupied through a maximum tilt angle
to a lower tilt position when the chair is occupied, said tilt axis
being disposed a substantial distance forwardly from and in
nonintersecting relationship to the vertical centerline of said
pedestal, the improvement wherein said tilt mechanism
comprises:
a housing structure mounted adjacent the upper end of said pedestal
and projecting forwardly therefrom toward the front edge of said
seat, said housing structure being substantially closed and
defining therein an interior compartment disposed between upper and
lower housing walls;
a support structure secured to said seat and projecting downwardly
therefrom adjacent but spaced slightly rearwardly from the front
edge thereof, said support structure having a hinge part which is
pivotally supported on said housing structure and defines said tilt
axis;
elongated lever means disposed within said compartment and having
one end thereof nonrotatably coupled to said hinge part so that
said lever means is pivotal about said tilt axis;
biasing means coacting between said housing structure and said
lever means for imposing a restoring force on said lever means and
hence a restoring torque about said tilt axis which urges said seat
toward said zero-tilt position, said biasing means cooperating with
said lever means so as to create a restoring torque which increases
approximately linearly as the seat tilts from the zero-tilt
position to an intermediate position but which deviates from and is
significantly less than the restoring torque which would be created
by extension of said linear relationship as the chair seat tilts
from said intermediate position to said lower tilt position;
said biasing means including bracket means secured to said housing
structure and defining a substantially upright wall, and a
compression-type spring means coacting between said lever means and
said housing structure for normally exerting a force against said
lever means tending to urge the latter towards said zero-tilt
position, said spring means having one end thereof remote from said
lever means supported for pivotal movement about a first generally
horizontal pivot axis which is parallel with said tilt axis and
stationarily related relative to said housing structure;
said biasing means also including cam means coacting between said
lever means, said spring means and said support bracket for
regulating the restoring torque in response to the seat tilt, said
cam means including first and second elongated cam profiles
respectively and stationarily associated with the lever means and
the support bracket, and a cam follower associated with the other
end of said spring means and cooperatively engaged and captivated
between said first and second cam profiles.
9. In a pedestal-type chair having a base assembly defining thereon
a pedestal which projects vertically upwardly in cantilevered
fashion, a seat structure having both a seat and a back, the seat
being disposed directly above the pedestal so that the latter has
its vertical centerline intersecting the seat adjacent the midpoint
thereof, and a knee-tilt mechanism connected between the pedestal
and seat and defining a substantially horizontally extending tilt
axis which extends sidewardly relative to the seat in the vicinity
of the front edge thereof for permitting the seat to be tilted
downwardly about the tilt axis from a substantially zero-tilt
position when the chair is unoccupied through a maximum tilt angle
to a lower tilt position when the chair is occupied, said tilt axis
being disposed a substantial distance forwardly from and in
nonintersecting relationship to the vertical centerline of said
pedestal, the improvement wherein said tilt mechanism
comprises:
a housing structure mounted on said pedestal adjacent the upper end
thereof and projecting forwardly therefrom toward the front edge of
said seat, and a support structure secured to said seat and
projecting downwardly therefrom adjacent but spaced slightly
rearwardly from the front edge thereof, said support and housing
structures having opposed parts which are relatively rotatably
supported on one another for defining said tilt axis;
first biasing means coacting between said hopusing and support
structures for imposing a first restoring torque about said tilt
axis which urges said seat toward said zero-tilt position, said
first biasing means defining a first torque-displacement
characteristic wherein the restoring torque increases approximately
lineraly as the seat tilts from the zero-tilt position into the
lower tilt position;
second biasing means coacting between said support and housing
structures for imposing a second restoring torque about said tilt
axis which urges said seat toward said zero-tilt position, said
second biasing means defining a second torque-displacement
characteristic wherein restoring torque decreases as the seat tilts
from the zero-tilt position into the lower tilt position; and
said first and second torque-displacement characteristics and the
torque generated thereby being additive as the seat is tilted away
from the zero-tilt position so as to definje a cumulative restoring
torque which increases as the seat is tilted toward the lower tilt
position.
10. A chair according to claim 9, wherein the first and second
biasing means respectively include first and second spring means
which are connected between said support and housing structures in
parallel relationship with respect to one another.
11. In a pedestal-type chair having a base assembly defining
thereon a pedestal which projects vertically upwardly in
cantilevered fashion, a seat structure having both a seat and a
back, the seat being disposed directly above the pedestal so that
the latter has its vertical centerline intersecting the seat
adjacent the midpoint thereof, and a knee-tilt mechanism connected
between the pedestal and seat and defining a substantially
horizontally extending tilt axis which extends sidewardly relative
to the seat in the vicinity of the front edge thereof for
permitting the seat to be tilted downwardly about the tilt axis
from a substantially zero-tilt position when the chair is
unoccupied through a maximum tilt angle to a lower tilt position
when the chair is occupied, said tilt axis being disposed a
substantial distance forwardly from and in nonintersecting
relationship to the vertical centerline of said pedestal, the
improvement wherein said tilt mechanism comprises:
a housing structure mounted on said pedestal adjacent the upper end
thereof and projecting forwardly therefrom toward the front edge of
said seat, and a support structure secured to said seat and
projecting downwardly therefrom adjacent but spaced slightly
rearwardly from the front edge thereof, said support and housing
structures having opposed parts which are relatively rotatably
supported on one another for defining said tilt axis; and
torque restoring means coacting between said housing and support
structures for imposing a restoring torque about said tilt axis
which urges said seat toward said zero-tilt position, said torque
restoring means including:
first means fixed relative to said support structure and defining
thereon a first elongate cam surface which extends generally
rearwardly of said seat away from said tilt axis,
second means fixed relative to said housing structure and defining
thereon a second elongate cam surface which extends in transverse
and intersecting relationship relative to said first elongate cam
surface,
cam follower means confined between and movable along said first
and second elongate cam surfaces, and
spring means continuously urging said cam follower means into
continuous engagement with both of said first and second elongate
cam surfaces and for imposing a restoring torque on said seat which
continuously urges it toward said zero-tilt position, said spring
means having one end thereof anchored to said cam follower means
and the other end thereof anchored to said support structure, said
other end being anchored to said support structure at a location
which is disposed rearwardly from said tilt axis.
12. A chair according to claim 11, wherein said first means
comprises an elongate lever which is fixed to said support
structure and is pivotally supported relative to said housing
structure for vertical pivoting movement about said tilt axis, said
first elongate cam surface extending longitudinally of said lever
in a direction which is generally radial with respect to said tilt
axis, said second elongate cam surface being elongated in a
direction which extends transversely with respect to both said
first elongate cam surface and the line of force generated by said
spring means.
13. In a pedestal-type chair having a base assembly defining
thereon a pedestal which projects vertically upwardly in
cantilevered fashion, a seat structure having both a seat and a
back, the seat being disposed directly above the pedestal so that
the latter has its vertical centerline intersecting the seat
adjacent the midpoint thereof, and a knee-tilt mechanism connected
between the pedestal and seat and defining a substantially
horizontally extending tilt axis which extends sidewardly relative
to the seat in the vicinity of the front edge thereof for
permitting the seat to be tilted downwardly about the tilt axis
from a substantially zero-tilt position when the chair is
unoccupied through a maximum tilt angle to a lower tilt position
when the chair is occupied, said tilt axis being disposed a
substantial distance forwardly from and in nonintersecting
relationship to the vertical centerline of said pedestal, the
improvement wherein said tilt mechanism comprises:
a housing structure mounted on said pedestal adjacent the upper end
thereof and projecting forwardly therefrom toward the front edge of
said seat, and a support structure secured to said seat and
projecting downwardly therefrom adjacent but spaced slightly
rearwardly from the front edge thereof, said support and housing
structures having opposed parts which are relatively rotatably
supported on one another for defining said tilt axis; and
biasing means coacting between said housing and support structures
for imposing a restoring torque about said tilt axis which
continuously urges said seat toward said zero-tilt position, said
biasing means defining a non-linear torque-displacement
characteristic as the seat tilts from the zero-tilt position into
the lower tilt position, said biasing means including:
an elongate lever fixed to one of said structures and supported
adjacent one end thereof for pivoting movement relative to the
other said structures about said tilt axis, said lever defining
thereon a first elongate reaction surface,
cam means fixed relative to said other structure and defining
thereon a second elongate reaction surface which extends in
generally intersecting relationship relative to said first reaction
surface,
follower means captively engaged between and movable along said
first and second reaction surfaces, and
spring means engaged with said follower means for maintaining said
follower means in engagement with said first and second reaction
surfaces so as to maintain a restoring torque on said lever which
varies in a nonlinear manner as the seat tilts away from the
zero-tilt position.
14. In a pedestal-type chair having a base assembly defining
thereon a pedestal which projects vertically upwardly in
cantilevered fashion, a seat structure having both a seat and a
back, the seat being disposed directly above the pedestal so that
the latter has its vertical centerline intersecting the seat
adjacent the midpoint thereof, and a knee-tilt mechanism connected
between the pedestal and seat and defining a substantially
horizontally extending tilt axis which extends sidewardly relative
to the seat in the vicinity of the front edge thereof for
permitting the seat to be tilted downwardly about the tilt axis
from a substantially zero-tilt position when the chair is
unoccupied through a maximum tilt angle to a lower tilt position
when the chair is occupied, said tilt axis being disposed a
substantial distance forwardly from and in nonintersecting
relationship to the vertical centerline of said pedestal, the
improvement wherein said tilt mechanism comprises:
a housing structure mounted on said pedestal adjacent the upper end
thereof and projecting forwardly therefrom toward the front edge of
said seat, and a support structure secured to said seat and
projecting downwardly therefrom adjacent but spaced slightly
rearwardly from the front edge thereof, said support and housing
structures having opposed parts which are relatively rotatably
supported on one another for defining said tilt axis; and
biasing means coacting between said housing and support structures
for imposing a restoring torque about said tilt axis which
continuously urges said seat toward said zero-tilt position, said
biasing means defining a non-linear torque-displacement
characteristic as the seat tilts from the zero-tilt position into
the lower tilt position, said biasing means including:
elongate lever means fixed to one of said structures and supported
for pivotal movement about said tilt axis relative to the other
said structure,
follower means carried by said lever means at a location spaced
radially outwardly from said tilt axis,
cam means defining thereon an elongate reaction surface which is
maintained in engagement with said follower means and defines a
path which comes progressively closer to said tilt axis as the
follower means engages said cam means and moves therealong away
from the zero-tilt position, and
spring means maintaining said follower means and cam means in
engagement with one another for imposing a restoring torque on said
lever means which increases from a minimum to a maximum along a
nonlinear path so that the torque increase per degree of lever
movement decreases as the lever means approaches a position
corresponding to the lower tilt position of the seat.
15. A chair according to claim 5, wherein said first cam profile is
of a substantially linear configuration and extends generally
radially of said levers, wherein said second cam profile is
substantially linear and extends in transverse and intersecting
relationship relative to said first cam profile, said second cam
profile also extending in transverse relationship relative to the
line of force created by said spring unit, and wherein said spring
unit comprises at least one coil-type spring.
16. A chair according to claim 7, wherein said spring unit includes
at least one coil-type spring, and wherein said first spring means
comprises a torsion-type spring which substantially surrounds said
tilt axis.
17. A chair according to claim 12, including second torque
restoring means coacting between said housing and support
structures for imposing a restoring torque about said tilt axis
which urges said seat toward said zero-tilt position, said second
torque restoring means being different from and cooperating in
parallel relationship with said first-mentioned torque restoring
means, said second torque restoring means including torsion-type
spring means coacting between said housing and said support
structures for generating a torque-displacement characteristic
which progressively increases as the seat is tilted away from the
zero-tilt position, the torque-displacement characteristic of said
second torque restoring means being significantly different from
the torque-displacement characteristic of said first-mentioned
torque restoring means.
18. A chair according to claim 13, including torque restoring means
coacting between said housing and support structures for imposing a
restoring torque about said tilt axis which continuously biases
said seat toward said zero-tilt position, said torque restoring
means being independent and different from said biasing means and
being disposed in parallel relationship therewith so that both said
biasing means and said torque restoring means impose a restoring
torque about said tilt axis, said torque restoring means creating a
restoring torque which varies approximately in a linear manner as
the seat tilts away from the zero-tilt position.
Description
FIELD OF THE INVENTION
This invention relates to an improved knee-type tilt mechanism for
a chair.
BACKGROUND OF THE INVENTION
Pedestal-type office chairs have conventionally utilized a
tilt-type control mechanism connecting the upper end of the
pedestal to the chair seat. This control mechanism defines a
substantially horizontal tilt axis which extends sidewardly across
the chair directly adjacent the underside thereof, with the tilt
axis being disposed substantially directly over the pedestal and
hence disposed substantially midway between the front and rear
edges of the chair seat. With this mechanism, rearward tilting of
the chair seat results in the rear edge of the seat swinging
downwardly, and simultaneously the front edge of the chair seat
lifts upwardly causing undesired lifting of the occupant's legs in
the vicinity of the knees. Tilt control mechanism of this type have
long possessed this recognized disadvantage, but have nevertheless
been extensively utilized in view of the difficulties in resolving
this problem.
In recent years chair manufacturers have succeeded in developing a
knee-tilt control mechanism. This mechanism connects to the upper
end of the pedestal but is positioned forwardly therefrom, whereby
the sidewardly extending horizontal tilt axis is disclosed more
closely adjacent the front edge of the chair seat. In this manner,
rearward tilting of the seat structure is accomplished solely by a
downward tilting of the rear edge of the seat, with the front edge
of the seat experiencing only minimal elevational change. The
occupant can thus experience tilting of the seat structure without
encountering undesired lifting of the legs away from the floor.
The design of a proper knee-tilt mechanism has presented several
formidable problems since such mechanism has to be cantilevered
forwardly from the upper end of the pedestal, and at the same time
the mechanism must be disposed within a package which does not ruin
the appearance of the chair.
Most attempts to provide a knee-tilt mechanism have employed a
spring-type restoring device using torsion or compression springs,
the latter cooperating with levers or a linkage for continually
urging the seat structure upwardly into its normal horizontal
position when unoccupied. These spring-type restoring devices have,
for the most part, created a restoring force which substantially
linearly increases as the tilt angle increases, the latter
typically being a minimum of about 15.degree. downwardly from the
horizontal or at rest position (i.e., the chair being unoccupied).
Because of the substantially linear relationship of the restoring
force, the known mechanism have possessed disadvantages which have
made use of these mechanisms, and the use and comfort of the chairs
employing them, less than desired.
For example, the known knee-tilt mechanisms have normally employed
a substantially linear restoring spring arrangement which possesses
a spring rate such that the restoring force increases significantly
as the seat structure is tilted backwardly. This significant
increase in the spring force is required so as to support the chair
occupant and counterbalance the backward tilt. If a low initial
torque and low spring rate are used, it has been observed that when
the occupant initially sits in the chair, the weight of the
occupant itself causes the seat structure to tilt backwardly
through a substantial extent, such as up to about 10.degree.. This
has been observed to be an undesirable degree of tilt since it
detracts from the chair comfort when working at a desk or table. A
rearward tilt in the range of 3.degree. to 5.degree. is preferred
under such circumstance.
To overcome this latter problem, several different structures have
been tried. The primary attempt has involved the use of a
mechanical lock which is manually controlled by the chair occupant.
That is, the knee( tilt mechanism is maintained with a spring
mechanism having properties of the type explained above, and in
addition the mechanism is provided with a manually controlled
mechanical lock. This lock is normally activated by the occupant
and, in effect, results in the chair seat being fixed in its
upright position, that is, the seat being oriented substantially
horizontally. When tilting of the seat is desired, the occupant has
to release the mechanical lock so that the tilt mechanism then
permits rearward tilting of the chair seat. Needless to say, the
provision of this mechanical lock greatly detracts from the comfort
and flexibility of the chair since the occupant must basically
always be converting the chair from a fixed to a tilt condition, or
vice versa, and this manual manipulation obviously detracts from
the desirability of the chair.
In other attempts to overcome this problem, other variations of the
tilt mechanism have used a higher spring rate, and/or have
increased the initial restoring force (i.e., the precompression or
pretorque) of the spring which maintains the unoccupied seat
structure in its horizontal position. Increasing the spring rate
and/or initial restoring force thus tends to counteract the initial
weight of the occupant. These changes, however, also cause the
linear relationship of the restoring force to be increased or
shifted upwardly throughout the complete tilt range so that, when a
person attempts to tilt the chair seat backwardly throughout
substantially its full range, it has been observed that many
occupants are unable to exert (at least comfortably) sufficient
force so as to permit rearward tilting of the chair throughout
substantially the full tilt angle. Under this circumstance, the
chair occupant again finds the chair highly uncomfortable due to
the inability to comfortably tilt backwardly the full extent, and
due to the excessively large restoring force which the occupant
must overcome.
Another commercial chair has attempted to overcome the above
problem by using a restoring mechanism which, while it employs a
spring having a substantially linear restoring force, nevertheless
the spring cooperates with a lever arm which, due to the angular
relationships involved, is intended to modify the restoring torque
and hence minimize the above-mentioned problem. Experience with
this known mechanism, however, indicates that the modification of
the restoring torque through use of this lever arm is so
insignificant as to be practically non-noticeable, and the overall
restoring mechanism still results in a restoring function which
possesses the same disadvantages.
Accordingly, it is an object of this invention to provide an
improved knee-tilt control mechanism which is believed to overcome
many of the disadvantages which have been associated with prior
structures as explained above. The knee-tilt control mechanism of
this invention is particularly of the passive type in that it does
not require any charge or action by the occupant, but rather
permits automatic reclining when desired.
More specifically, it is an object of this invention to provide an
improved knee-tilt control mechanism which provides a substantially
nonlinear restoring torque throughout the angle of tilt so as to
provide adequate stiffness to maintain the chair seat at a desired
position under normal use conditions with an occupant therein,
while at the same time permitting the chair to be tilted rearwardly
throughout substantially its full range without generating an
excessively large restoring torque which make tilting difficult or
uncomfortable.
In a preferred embodiment of this improved kneetilt control, the
nonlinear restoring torque preferably includes a substantially
linearly increasing restoring torque over the initial range of tilt
such as from the 0.degree. position to about the 5.degree.
position, with the restoring torque thereafter undergoing a "dwell"
or minimal change during further chair tilt so as to prevent the
maximum restoring torque at the full tilt angle from reaching an
excessive magnitude.
In the improved mechanism of this invention, as aforesaid, the
initial restoring torque, and the increasing restoring torque as
the chair seat tilts rearwardly due to the weight of the occupant,
is such as to maintain the chair seat at only a small rearward tilt
angle with respect to the horizontal, such as a maximum tilt angle
of about 3.degree. to 5.degree., to hence maintain an optimum
seating position for the occupant. At the same time, rearward
tilting of the seat throughout its full range can be easily
accomplished, even by a person of rather light weight, without
encountering excessive restoring torque which makes such tilting
uncomfortable or impossible.
A further object is to provide an improved mechanism, as aforesaid,
which is relatively compact and hence can be structurally and
properly designed so as to be positioned directly under the front
portion of the chair seat without detracting from the overall
esthetics or appearance of the chair. This improved mechanism also
possesses the capability of permitting the initial restoring torque
to be selectively adjusted without requiring any complex adjustment
function or disassembly of the mechanism.
According to one embodiment of the present invention, the seat
structure and pedestal of a chair are joined together by a
knee-tilt control mechanism which includes a first support which is
fixed to and projects downwardly from the underside of the chair
seat adjacent the front edge thereof, and a second support which is
fixed to the upper end of the pedestal and projects forwardly
therefrom so as to terminate in a generally sidewardly extending
tubelike structure. The first support has a pair of bearing hubs at
opposite ends which are rotatably engaged with the tubelike
structure so as to define a horizontal tilt axis which extends
sidewardly of the chair seat and is disposed closely adjacent the
underside thereof in close proximity to the front edge. A
spring-type restoring mechanism coacts between the first and second
supports for exerting a restoring moment or torque which
continuously urges the chair seat upwardly into a substantially
horizontal (i.e., zero tilt) position. The restoring mechanism
preferably includes a first spring unit, such as a torsion spring,
which develops a restoring torque which increases substantially
linearly as the tilt of the chair seat increases from the zero-tilt
to the maximum tilt position. The pretorque of this first spring
unit can be adjusted to select the restoring torque which is
imposed on the chair at the zero tilt position. The restoring
mechanism employs a second spring unit which cooperates in
generally parallel relationship to the first spring unit and, while
the second spring unit develops a restoring torque which also
increases approximately linearly as the chair tilts away from the
zero tilt position to an intermediate position of about 5.degree.,
the restoring torque generated by this mechanism throughout the
remaining range of tilt thereafter deviates from the initial
linearity so that the total restoring torque hence exhibits a
"dwell" effect substantially at the intermediate location. To
achieve this nonlinear torque relationship throughout its tilt
range, the second spring unit employs a spring which cooperates
with a cam profile, the latter in turn being associated with a
swingable lever so that the force or compression in the spring
increases only up to about the intermediate location, after which
the compression force in the spring remains substantially constant
or continues to increase but only at a significantly lower rate in
relationship to the rate of tilt. In addition, due to the
positional relationship between the cam and lever when the tilt
exceeds the intermediate location, the compression force of the
spring acts through a smaller lever arm such that the first spring
unit exerts a reduced restoring torque as the tilt angle increases,
thus minimizing the build-up in combined restoring torque as the
tilt angle reaches its maximum.
According to another embodiment of the invention, the second spring
unit again cooperates in generally parallel relationship to the
first spring unit so that the restoring torque is the sum of the
torques generated by the first and second spring units. The second
spring unit, however, develops a restoring torque which is a
maximum at the zero-tilt position, and this restoring torque
remains fairly constant throughout the initial tilt up to about
4.degree. or 5.degree., and thereafter progressively decreases
throughout the full angle of tilt. The total restoring torque
generated by the first and second spring units thus increases
generally linearly from the zero-tilt position to an intermediate
position of about 5.degree., with the total restoring torque
continuing to increase throughout the full tilt angle but doing so
at a continually decreasing rate so that the maximum restoring
torque as developed when the chair seat reaches its full tilt angle
is of a magnitude which does not interfere with the comfort and
convenience of use of the chair.
Other objects and purposes of the invention will be apparent upon
reading the following specification and inspecting the
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 and 2 diagrammatically illustrate side and front
elevational views, respectively, of a pedestal-type chair employing
the improved knee-tilt control mechanism of invention.
FIG. 3 is a side elevational view of the knee-tilt control
mechanism, partially in cross section, as taken substantially along
line III--III in FIG. 4.
FIG. 4 is a fragmentary view as taken substantially along line
IV--IV in FIG. 3.
FIG. 5 is a fragmentary sectional view as taken substantially along
line V--V in FIG. 4.
FIG. 6 is a sectional view, on an enlarged scale, illustrating the
relationship of the nonlinear restoring mechanism, the spring being
removed for clarity of illustration.
FIG. 7 illustrates, on an enlarged scale, the cooperating cam
profiles.
FIG. 8 diagramatically illustrates the relationship between torque
and tilt angle associated with the mechanism of FIGS. 3-7.
FIGS. 9-11 are views which respectively correspond to FIGS. 6-8 but
illustrate a preferred variation of the invention.
Certain terminology will be used in the following description for
convenience in reference only, and will not be limiting. For
example, the words "upwardly", "downwardly", "rightwardly" and
"leftwardly" will refer to directions in the drawings to which
reference is made. The words "inwardly" and "outwardly" will refer
to directions toward and away from, respectively, the geometric
center of the chair and designated parts thereof. Said terminology
will include the words specifically mentioned, derivatives thereof,
and words of similar import.
DETAILED DESCRIPTION
FIGS. 1 and 2 illustrate a pedestal-type chair 10 having a seat
structure 11 supported on a pedestal-type base assembly 12. The
seat structure 11 includes a back 13 integrally joined to a seat
14, although the seat and back could be separate as is
conventional. The base assembly 12 includes a wheeled five-star
base which is generally conventional and has a central pedestal 16
projecting vertically upwardly therefrom, which pedestal defines a
vertical swivel axis 17 which intersects approximately at the
center of the seat 14.
In the improved chair of the present invention, the pedestal 16 and
seat 14 are joined together by a tilt or pivot mechanism 18 of the
knee-joint type, which mechanism 18 defines a generally
horizontally extending tilt axis 19 which extends transversely
(i.e., sidewardly) of the seat 14 and is disposed in forwardly
spaced relationship from the swivel axis 17 so as to be positioned
more closely adjacent the front edge of the seat 14 while being
disposed vertically directly thereunder.
The tilt mechanism 18 is spring biased so as to normally maintain
the seat 14 in a substantially 0.degree. tilt (i.e. zero tilt)
position as illustrated by FIG. 1, in which position the seat 14
extends approximately horizontally from front-to-back. Under load,
however, such as created by an occupant sitting in the chair, the
seat 14 (and in fact the entire seat structure 13) can tilt
backwardly and downwardly about the tilt axis 19 through a limited
tilt angle which generally is a minimum of about 15.degree.. This
minimum tilt is diagrammatically illustrated by dotted lines in
FIG. 1.
The tilt mechanism 18 (FIG. 3) includes a housing structure 21
which is mounted on the upper end of the pedestal 16 and projects
forwardly therefrom, which housing structure in turn rotatably
supports thereon a support structure 22 for relative tilting about
the axis 19. This support structure 22 in turn is fixedly secured
to a frame (not shown) which is disposed internally of the seat 14,
with the support structure 22 projecting downwardly below the
bottom shell or pan which encloses the seat 14. First and second
spring-type biasing means 23 and 24 coact between the housing
structure 21 and the support structure 22 for imposing a biasing or
restoring torque on the support structure 22, and hence on the seat
14, so as normally maintain the latter in the horizontal or
zero-tilt position. A pretorque adjusting means 25 cooperates with
the biasing means 23 for defining a base or initial torque which
continuously acts against the support structure 22 and seat 14 so
as to maintain it in its zero-tilt position.
Considering now the details of the tilt mechanism 18 as shown by
FIGS. 3-5, the housing structure 21 includes top and bottom cover
plates 26 and 27 which are approximately of triangular shape and
are rigidly joined together at their apex so as to define a hub 28,
the latter being telescoped over the upper end of the pedestal 16.
The housing 21 projects forwardly from this hub 28 toward the front
free edge of the seat 14, and the forward edges of the plates 26-27
are rigidly joined to a horizontally elongated front wall 29 which
extends transversely relative to the seat slightly therebelow and
spaced inwardly a small distance from the front edge thereof. This
front wall 29 extends between and is rigidly joined to a pair of
sidewardly spaced sleevelike hubs or tubes 31. These tubes 31 are
axially aligned and define the tilt axis 19.
The support structure 22 is pivotally or hingedly supported on the
housing structure 21, and for this purpose includes a pair of
mounting brackets 32 which have parallel upper plate portions 33
which are sidewardly spaced apart and disposed within the interior
of the seat 14, these plate portions 33 being rigidly secured to
the interior frame (not shown) of the seat. The plate portions 33
extend approximately horizontally when in the zero-tilt position,
and at their outer edges are provided with downwardly projecting
arms 34, the latter terminating in inwardly opposed and coaxially
aligned cylindrical hubs 35 which are rotatably received within the
ends of the tubes 31. The hubs 35 are nonrotatably fixed to
opposite ends of a shaft 36 which extends through tubes 31 along
the axis 19.
Considering now the first biasing means 23, it includes a spring
41, the latter preferably comprising a torsion spring formed of an
elastomeric or rubberlike material. This torsion spring 41 is
formed substantially as an axially elongated hollow tube or sleeve
disposed in surrounding relationship to and nonrotatably secured,
as by bonding, to a metal sleeve 40. This sleeve 40 has a hole
extending axially therethrough, which hole is of a noncircular
(i.e., hexagonal) cross section in the preferred embodiment and
snugly accommodates therein the metal shaft 36 which is also of
hexagonal cross section so as to be nonrotatably coupled to the
sleeve 40. The sleeve spring 41 is also nonrotatably coupled to a
radially outwardly projecting lever 42. This lever 42 has, at its
inner end, a sleevelike hub 43 which surrounds the elastomeric
spring 41 and is nonrotatably coupled to the outer peripheral wall
thereof.
The lever 42 is normally maintained in a stationary position
relative to the housing structure 21, and for this purpose the
lever 42 adjacent its outer end cooperates with the pretorque
adjusting means 25. The latter includes an adjusting shaft 45 which
is threadably rotatably supported on the bottom wall 27 so as to
project outwardly therebelow. A knob 46 is nonrotatably secured to
the outer or lower end of this threaded adjusting shaft 45. The
inner or upper end of this shaft 46 abuts the underside of the
lever 42 so as to normally maintain the latter in a stationary
position relative to the housing structure 21. When the chair seat
is tilted backwardly away from its zero-tilt position, the shaft 36
rotates counterclockwise in FIG. 3 so as to torque the elastomeric
spring sleeve 41 inasmuch as the lever 42 and sleeve 43 hold the
outer periphery of the elastomeric spring 41 stationary. The torque
generated by the sleeve spring 41 hence increases approximately
linearly substantially as illustrated by the torque T.sub.1 as
graphed in FIG. 8. The initial or pretorque T.sub.0 of this spring
41 can be adjusted by rotating the knob 46 and shaft 45 so as to
move the latter upwardly, and hence lift the lever 42 upwardly
(clockwise in FIG. 3). This causes the spring sleeve 41 to be
pretorqued in the direction opposite to that caused when the chair
seat is tilted, and thus increases the restoring torque T.sub.0
which exists at the zero-tilt position.
The use of an elastomeric sleevelike torsion spring, oftentimes
referred to as a "rubber pack", is well known and it will be
appreciated that the torque developed by the elastomeric spring 41
in response to increased angular distortion thereof will not
necessarily follow a perfect linear relationship in view of the
fact that such characteristic can vary due to the specific
properties of the elastomeric material.
Considering now the second biasing means 24, it includes a spring
unit 51 which is defined by a pair of conventional coil-type
compression springs 52 disposed in parallel, which compression
springs are confined between relatively movable upper and lower
retainers 53 and 54, respectively. Each of the compression springs
52 preferably comprises, in the illustrated embodiment, concentric
inner and outer coil springs so as to increase the spring force
capacity. The lower retainer is secured to a lower transversely
extending hinge pin 55 which is pivotally supported on a bracket
56.
The bracket 56 is disposed within the housing structure 21 between
the upper and lower plates thereof, and is of a generally U-shaped
or channel-shaped configuration in that it includes a bight plate
57 having a pair of substantially parallel side plates or arms 58
projecting upwardly from opposite ends thereof. The bight 57
overlies and is suitably fixedly secured to the bottom plate
27.
The lower pivot pin 55 as associated with the lower retainer 54 has
the opposite ends thereof suitably pivotally supported on the side
plates 58, whereby the lower pivot pin 55 hence defines a pivot
axis which extends generally parallel with the tilt axis 19.
The upper retainer 53 also has a pivot pin 59 mounted thereto and
extending transversely thereof, this pin 59 being generally
parallel with the lower pin 55. The upper pivot pin 59 extends
transversely between and through the side plates 58, and for this
purpose the side plates 58 have identical cam slots 61 formed
therein and through which pass the outer ends of the upper pivot
pin 59. The pivot pin 59 has suitable rollers 62 (FIG. 6) thereon
which are confined and rollingly engaged within the cam slots
61.
The second biasing means 24 also includes a pair of levers 63 which
cooperate with the spring unit 51 for controlling the position and
compression thereof. These levers 63 project radially outwardly
from the tilt axis 19 in generally parallel relationship. The
levers 63, at their radially inner ends, are provided with support
hubs 64 which are nonrotatably secured to the shaft 36 and are
loosely rotatably positioned within the tubes 31. These hubs 64 are
disposed adjacent opposite ends of, and hence straddle, the
elastomeric sleeve spring 41. The levers 63 as they project
radially outwardly from the hubs 64 are also disposed so as to
straddle the bracket 56, with each lever 63 being disposed closely
adjacent an outer side surface of one of the side plates 58. Each
of these levers 63 has a cam slot 65 (FIG. 6) formed therein
adjacent the free end thereof, and this cam slot 65 movably
confines therein the outer end of the upper pivot shaft 59. The end
of shaft 59 preferably has a cam roller thereon confined for
rolling engagement within the slot 65.
The cam slot 65 has a profile which, as indicated by the line 66 in
FIG. 7, extends generally radially of the lever 63 relative to the
tilt axis 19.
Considering now the profile of the cam slot 61, this has a profile
which is nonlinear as indicated by the dash-double dot line 67.
This profile 67 includes a first substantially linear profile 68
which extends from the zero-tilt position to an intermediate
position which is a tilt of approximately 5.degree., at which
intermediate position there is then defined a second profile 69
which extends to the full tilt angle which is a maximum of about
15.degree. to 26.degree.. The first and second profile portions 68
and 69 are joined together through a smooth transition curve.
The second profile portion 69 preferably has a nonlinear
relationship and, in the illustrated embodiment, is defined by an
arc generated substantially about an axis 60 which is parallel to
but spaced sidewardly from the axis of the lower pivot pin 55. In
fact, the axis 60 and the axis of pivot pin 55 are both preferably
spaced equally from the uppermost end of the profile portion 69,
which uppermost end is graphically defined by the point 70 in FIG.
7. Since profile portion 69 is generated about axis 60 in a
downward swinging direction away from the point 70, this hence
causes the profile portion 69 to continuously and progressively
move closer to the axis 55 as the profile portion 69 is generated
downwardly toward its free or lower end. The axis 60 and the
profile portion 69 are disposed on opposite sides of an imaginary
vertical plane 71 which extends through and contains the axes of
the pivot pins 55 and 59 when the pivot pin 59 is disposed in the
upper end of the profile portion 68 corresponding to the zero-tilt
position.
The first profile portion 68 extends transversely relative to the
radial direction 70 between the upper and lower pivot pins 55 and
59 respectively, and this first profile portion 68 also extends
transversely relative to the radial direction (as represented by
the line 66) of the lever 63. In fact, in the range of movement of
lever 63 between the zero-tilt position and its intermediate
position (of substantially 5.degree. tilt), the first profile 68
very nearly perpendicularly intersects the profile 66.
When the chair seat 14 is in its zero-tilt position, the second
biasing means 24 occupies the position substantially as illustrated
in the drawings, and hence the spring unit 51 is subject to some
initial compression so that this acts against the levers 63 so as
to exert an initial or pretorque T.sub.0 ' for assisting in
maintaining the chair seat in its zero-tilt position. As the chair
seat is tilted from its zero-tilt position to an intermediate tilt
position of approximately 5.degree., this causes the cam levers 63
to rotate downwardly (counterclockwise) forcing the upper pivot pin
59 to slide downwardly along the upper cam profile 68 of the slot
61, and simultaneously slide radially inwardly of the cam slot 65.
This hence causes the compression of the spring unit 51 to
substantially linearly increase, and the torque imposed about the
tilt axis 19 also substantially linearly increases approximately as
diagrammatically illustrated by the dash-dot line T.sub.2 in FIG.
8. Upon reaching the intermediate position, however, further
downward tilt of the chair and of the levers 63 causes the upper
pivot pin 59 to pass through the transition into the upper end of
the second profile 69. Since profile 69 is effectively generated
about the lower pivot 55, this effectively results in the force of
the spring pack 51 being effectively confined by the bracket 56,
and hence the spring force exerted on the levers 63 decreases
significantly, thereby also causing the restoring torque as
generated by this second biasing means 24 to significantly decrease
throughout the remaining angle of tilt as diagrammatically
illustrated by FIG. 8.
Since the restoring torque imposed on the chair seat is the sum of
the torques generated by the first and second biasing means 23 and
24 respectively, this total torque hence effectively has a pattern
which is diagrammatically approximated by the solid line T.sub.3 in
FIG. 8. That is, the torque will initially increase at a
substantially steep and approximately linear rate as the chair seat
tilts away from the zero-tilt position, and hence this will enable
the chair seat to move into a position of about 2.degree. to about
3.degree., which position is optimum for normal support of the
occupant's weight. Further, the tilt torque will continue to
increase significantly so that the occupant can tilt the chair back
to an angle of about 5.degree., at which time the restoring torque
no longer increases significantly at this intermediate location,
but rather undergoes a dwell or slight decrease, following which
the restoring torque will then again thereafter increase (but at a
lesser rate) until reaching the maximum tilt position. In this
manner, after passing through this intermediate "dwell" location,
the occupant will again feel an increase in restoring torque as he
tilts backward toward the full tilt position, but at the same time
the restoring torque which the occupant must overcome is of such
magnitude as to permit the occupant to tilt the chair to the full
tilt position without causing the tilting operation to be
uncomfortable or stressful.
While the embodiment described above utilizes the cam slot 61 for
controlling movement of the upper hinge pin 59 and corresponding
movement of the lever 63, it will be appreciated that in actuality
it is the upper edge 72 of the cam slot 61 which effectively
controls movement of the upper pivot pin 59. This upper edge 72
defines the cam profile which controls the movement of the upper
pivot pin 59, and hence controls the movement of the lever 63. Use
of the closed slot 61 is preferred, however, so as to provide
positive control over the pin 59 in all positions of use.
Referring now to FIGS. 9-11, there is illustrated a preferred
variation of the present invention wherein corresponding parts are
designated by the same reference numerals utilized above, except
that the reference numerals utilized to illustrate parts which have
been modified additionally have a prime (') used in conjunction
therewith so as to distinguish the modified parts from those parts
which have been described above.
According to the modifications shown by FIGS. 9-11 (which figures
respectively correspond to FIGS. 6-8 above), the cam slot 61' as
formed in the bracket 56 has a profile which is linear throughout
its length as indicated by the dash-double dot line 67'. This
linear profile 67' extends from the zero-tilt position as
represented by the position of the upper pivot pin 59 in FIGS. 9
and 10, through the intermediate position to the full tilt angle.
The profile 67' extends in transverse relationship to the radial
direction 66 of the lever slot 65, and also extends in transverse
relation to the plane 71 when the upper pivot pin 59 is in the
zero-tilt position. These transverse relationships are preferably
nonperpendicular with respect to the line 66 and plane 71, and in
fact in the preferred embodiment the profile 67' approximately
bisects the angle defined between the line 66 and plane 71 when in
the zero-tilt position. It is also essential that the radial line
61 and the plane 71, when in the zero-tilt position, themselves
extend in transverse intersecting relationship to one another,
which relationship defines an included angle therebetween in the
range of about 120.degree. to about 135.degree..
In this embodiment of FIGS. 9-11, the upper edge 72 is the cam
profile which controls the upper pivot pin 59, and thus provision
of the closed slot 61' is solely for purposes of convenience to
optimize control of the pin 59 under all conditions of use.
With this embodiment of FIGS. 9-11, the overall tilt mechanism
works in a very similar manner to that described above. More
specifically, the restoring torque follows a pattern which is
diagrammatically illustrated by FIG. 11. That is, the torque
T.sub.1 ' designates the linearly increasing restoring torque
generated by the main spring unit 23 as the chair seat tilts
backwardly through its full tilt angle. On the other hand,
according to the embodiment of FIGS. 9-11, the secondary biasing
means 24 generates a torque having a pattern which more closely
resembles that illustrated by the dash-dot line T.sub.2 ' as
appearing in FIG. 11. This restoring torque T.sub.2 ' starts at an
initial pretorque corresponding to the zero-tilt position, and the
restoring torque T.sub.2 ' remains fairly constant or uniform at
this initial pretorque level throughout the initial chair tilt up
to about 4.degree. or 5.degree.. Thereafter the restoring torque
T.sub.2 ' progressively and continuously decreases throughout the
remainder of the full tilt angle, and in fact the restoring torque
T.sub.2 ' deceases at an increasing rate as the chair seat
approaches the full tilt angle. Hence, the combined restoring
torque T.sub.3 ' which is imposed on the chair seat is thus the sum
of the torques T.sub.1 ' and T.sub.2 '. This restoring torque
T.sub.3 ' starts with the pretorque at the zero-tilt position, and
thereafter increases fairly linearly up to the intermediate
position of about 5.degree. , and from that point on the restoring
torque T.sub.3, continues to increase throughout the full angle of
tilt, but continues to increase at a decreasing rate so that the
total restoring torque T.sub.3 ' at the full tilt angle exhibits a
curve which tends to flatten out. Thus, the overall effect is to
provide a restoring torque which can have an initial pretorque of a
magnitude sufficient to prevent excessive tilt of the chair seat
under the normal occupant weight, which will still have a fairly
linearly and desirably increasing restoring torque up to about the
5.degree. position so as to permit normal use of the chair without
encountering excessive tilt, and which will also permit the chair
to be readily tilted throughout its full tilt angle while at the
same time generating a restoring torque which continuously
increases throughout the full tilt angle but does so at such a rate
as to permit full tilt to be readily and comfortably accomplished
by the chair occupant.
Although particular preferred embodiments of the invention have
been disclosed in detail for illustrative purposes, it will be
recognized that variations or modifications of the disclosed
apparatus, including the rearrangement of parts, lie within the
scope of the present invention.
* * * * *